This invention relates to an autosampler which detects air bubbles in specimen and, more particularly, to an autosampler used in liquid chromatograph or automatic chemical analyzer to check whether the liquid sample has been drawn from a sample container into the analyzing apparatus without bubbles, being mixed therein.
Conventional autosamplers known which detect by use of a sensor air bubbles mixed in the liquid specimen to be analyzed and then remove the air bubbles from the liquid specimen.
The Japanese Patent Laid-Open No. 167470/1987 describes a method of removing the air portion from the specimen by detecting the air portion in the liquid specimen drawn in through a needle from a specimen container and by removing the air bubble from the liquid specimen analyzing passage.
In this method, the specimen taken in from the needle is fed through a long passage to a 6-way valve, and at the inlet thereof the air bubbles are detected. Thus, the air bubbles cannot be detected without taking in a significant amount of specimen from the needle. And when the air portion in the liquid specimen is to be removed from the needle, a large amount of the liquid specimen has to be discarded along with the air bubble.
Furthermore, since the air portion in the liquid specimen is detected in a wide passage at the inlet of the 6-way valve, the fine air bubbles are very difficult to detected. While the detection may be made possible by narrowing the inlet, this will also increase the flow speed of specimen making it difficult to discharge the unwanted air-mixed specimen at an appropriate timing by changing the slow-response 6-way valve. Therefore, the above air detection method is not suitable for the autosampler that makes analysis and measurement of a very small amount of specimen which may easily trap fine bubbles.
The Japanese Patent Laid-Open No. 132064/1982 and 275659/1986 describe a method of detecting air bubbles by installing electrodes in a tube connected to a suction nozzle through which the liquid specimen is drawn in and by checking changes in electrostatic capacitance. This method, too, has a long passage from the specimen suction point to the air detecting point and therefore has similar drawbacks to those stated above.
Therefore, in these conventional techniques, it is difficult to detect fine bubbles that were mixed in a very small amount of specimen when the specimen was drawn in by suction. If the bubbles are detected, the conventional techniques have a problem of having to discharge a significant amount of the liquid specimen in order to remove the air portion such as air bubbles.
In the Japanese Patent Laid-Open No. 85355/1985, a method is disclosed for checking the specimen optically at a location near the nozzle. This method, however, is to check the concentration of a chemical substance in the specimen and is not used to detect the air bubbles contained in the specimen solution.